There has been known a Solid Oxide Fuel Cell (SOFC) where anode gas is supplied to one side and cathode gas (air and similar gas) is supplied to the other side to be configured to operate at a relatively high temperature. This SOFC uses a water-containing fuel such as water-containing ethanol. Since the fuel contained in such a water-containing fuel is easily evaporated compared with water, a moisture content of the water-containing fuel increases in a fuel tank. Using such a water-containing fuel having the high moisture content possibly reduces a power generation performance of the fuel cell.
Therefore, for example, JP2010-190210A discloses a technique where the fuel evaporated in the fuel tank is liquefied again to be recovered and the liquefied fuel is returned to the fuel tank.